Group Goes to Bat for Silverspot Butterfly

SAN MATEO, Calif. (CN) – Development threatens one of last remaining callipe silverspot butterfly populations, environmentalists say. The endangered butterfly depends upon a single plant species to survive – the yellow pansy – and a San Bruno Mountain housing complex would drastically reduce a vital corridor for the insect, San Bruno Mountain Watch says.

Mountain Watch challenges San Mateo County’s changes to a habitat conservation plan, formulated after the butterfly was listed as endangered in 1997. The callipe silverspot butterfly depends upon the yellow pansy, upon which it feeds and lays eggs. In springtime, larvae molt four times and then spend their pupal stage in nests of leaves glued together with silk.A habitat conservation plan failed to mitigate loss of the host plant, for which domestic cultivation has been fruitless, the group says. The plan amendment, approved in 2007, would allow the Northeast Ridge housing development to modify almost 17 acres of habitat, and temporarily alter another 3 acres would be temporarily altered. That will fragment and isolate the butterfly population, by narrowing a vital dispersal corridor that allows it to find and breed with other populations on the mountain, the group says. The group also cites concerns over funding for habitat management and reliance upon baseline conditions dating from 1989. San Bruno Mountain Watch wants the county to conduct a complete environmental impact report. Bruno Mountain is the “largest and richest remaining native Franciscan bioregion” for the butterfly. The callipe silverspot butterflies there are the only ones on the San Francisco peninsula, and one of two such populations in the region. The butterflies are represented in San Mateo County Court by Paul Carroll of Redwood City.